Atmospheric particulate matter with diameter <2.5 um (PM2.5) was collected at Peking University (PKU) in Beijing, China before, during, and after the 2008 Olympics and analyzed for black carbon (BC), organic carbon (OC), lower molecular weight (MW<300) and MW302 Polycyclic Aromatic Hydrocarbons (PAHs), nitrated PAHs (NPAHs) and oxygenated PAHs (OPAHs). In addition, the direct and indirect acting mutagenicity of the PM2.5 and the potential for DNA damage to human lung cells were also measured. Significant reductions in BC (45%), OC (31%), MW< 300 PAH (26% – 73%), MW 302 PAH (22% – 77%), NPAH (15% – 68%) and OPAH (25% – 53%) concentrations were measured during the source control and Olympic Olympic period. However, the mutagenicity of the PM2.5 was significantly reduced only during the Olympic period. The PAH, NPAH, and OPAH composition of the PM2.5 was similar throughout the study, suggesting similar sources during the different periods. During the source control period, the parent PAH concentrations were correlated with NO, CO, and SO2 concentrations, indicating that these PAHs were associated with both local and regional emissions. However, the NPAH and OPAH concentrations were only correlated with the NO concentrations, indicating that the NPAH and OPAH were primarily associated with local emissions. The relatively high 2-nitrofluoranthene/1-nitropyrene ratio (25 – 46) and 2-nitrofluoranthene/2-nitropyrene ratio (3.4 – 4.8), suggested a predominance of photochemical formation of NPAHs through OH-radical-initiated reactions in the atmosphere. On average, the ΣNPAH and ΣOPAH concentrations were 8% of the parent PAH concentrations, while the direct-acting mutagenicity (due to the NPAH and OPAH) was 200% higher than the indirect-acting mutagenicity (due to the PAH). This suggests that NPAH and OPAH make up a significant portion of the overall mutagenicity of PM2.5 in Beijing.

Wide bandgap (WB) organic-inorganic hybrid perovskites (OIHPs) with a bandgap ranging between 1.7 and 2.0 eV have shown great potential to improve the efficiency of single-junction silicon or thin-film solar cells by forming a tandem structure with one of these cells or with a narrow bandgap perovskite cell. However, WB-OIHPs suffer from a large opencircuit voltage (V oc ) deficit in photovoltaic devices, which is associated with the phase segregation of the materials under light illumination. In this work the photoinstability is demonstrated and V oc loss can be addressed by combining grain crystallization and grain boundary passivation, achieved simultaneously through tuning of perovskite precursor composition. Using FA 0.17 Cs 0.83 PbI 3-x Br x (x = 0.8, 1.2 1.5, and 1.8), with a varied bandgap from 1.72 to 1.93 eV, as the model system it is illustrated how precursor additive Pb(SCN) 2 should be matched with a proper ratio of FAX (I and Br) to realize large grains with defect-healed grain boundaries. The optimized WB-OIHPs show good photostability at both room-temperature and elevated temperature. Moreover, the corresponding solar cells exhibit excellent photovoltaic performances with the champion V oc /stabilized power output efficiency reaching 1.244 V/18.60%, 1.284 V/16.51%, 1.296 V/15.01%, and 1.312 V/14.35% for WB-OIHPs with x = 0.8, 1.2, 1.5, and 1.8, respectively.

sivation), [18,19] the record EQEs of PeLEDs have reached 12.3%, [20] 28.1%, [21] 23%, [22] and 22.2% [23] for blue, green, red, and infrared emission, respectively. Despite the remarkable progress in improving the performance of PeLEDs, the devices still suffer from poor operational stability and rapid decay over time. Although encapsulation of the devices can protect them against moisture and oxygen, [24] internal heat-or electric field-driven defect generation processes, which are often linked to ion migration, could cause severe degradation of electroluminescence.Ion motion in MHPs was initially observed in perovskite solar cells (PSCs) and manifested as an anomalous dielectric response at low frequency and hysteresis in the current-voltage curve. [25] Extensive studies have been performed to investigate the properties of the ions, [25,26] the ion distribution in PSCs under dark and illumination, [27] and the electronic-ionic coupling and its impact on device operation. [28] PSCs differ from PeLEDs in that the fabrication of PeLEDs typically involves the use of largely excess organic halide salts; a portion of these halides do not participate in the perovskite lattice but instead reside on the surfaces and grain boundaries, thus inducing additional mobile ions in the PeLEDs. [29][30][31] More importantly, the electric field across the very thin perovskite layer (typically tens of nanometers) in a PeLED is much stronger than the field in a PSC. Because of these factors and the effects of local heating, ion migration has a substantial effect on PeLEDs operation. Indeed, numerous recent studies have reported ion-induced degradation of PeLEDs. [31][32][33][34][35][36] Accordingly, many studies on understanding, characterizing, and preventing ion generation and migration in PeLEDs have been performed in the last few years.Herein, we perform a systematic review of the origin, movement mechanism, characterization, effects on device performance and stability, and management of ion migration in PeLEDs. As presented in Scheme 1, the review begins by introducing the origins of ionic defects by considering the structural, compositional, and processing characteristics of perovskite emissive layers. Then, the transport dynamics of ions are described with a focus on three factors: Migration activation energy, external stimulus (e.g., electric field and Joule heating), and pathways (i.e., bulk vs grain boundaries or surfaces). Third, the characterization approaches for probing ion migration in In recent years, perovskite light-emitting diodes (PeLEDs) have emerged as a promising new lighting technology with high external quantum efficiency, color purity, and wavelength tunability, as well as, low-temperature processability. However, the operational stability of PeLEDs is still insufficient for their commercialization. The generation and migration of ionic species in metal halide perovskites has been widely acknowledged as the primary factor causing the performance degradation of PeLEDs. Herein, this topic is systematically d...

BackgroundThe 2008 Beijing Olympic Games provided a unique case study to investigate the effect of source control measures on the reduction in air pollution, and associated inhalation cancer risk, in a Chinese megacity.ObjectivesWe measured 17 carcinogenic polycyclic aromatic hydrocarbons (PAHs) and estimated the lifetime excess inhalation cancer risk during different periods of the Beijing Olympic Games, to assess the effectiveness of source control measures in reducing PAH-induced inhalation cancer risks.MethodsPAH concentrations were measured in samples of particulate matter ≤ 2.5 μm in aerodynamic diameter (PM2.5) collected during the Beijing Olympic Games, and the associated inhalation cancer risks were estimated using a point-estimate approach based on relative potency factors.ResultsWe estimated the number of lifetime excess cancer cases due to exposure to the 17 carcinogenic PAHs [12 priority pollutant PAHs and five high-molecular-weight (302 Da) PAHs (MW 302 PAHs)] to range from 6.5 to 518 per million people for the source control period concentrations and from 12.2 to 964 per million people for the nonsource control period concentrations. This would correspond to a 46% reduction in estimated inhalation cancer risk due to source control measures, if these measures were sustained over time. Benzo[b]fluoranthene, dibenz[a,h]anthracene, benzo[a]pyrene, and dibenzo[a,l]pyrene were the most carcinogenic PAH species evaluated. Total excess inhalation cancer risk would be underestimated by 23% if we did not include the five MW 302 PAHs in the risk calculation.ConclusionsSource control measures, such as those imposed during the 2008 Beijing Olympics, can significantly reduce the inhalation cancer risk associated with PAH exposure in Chinese megacities similar to Beijing. MW 302 PAHs are a significant contributor to the estimated overall inhalation cancer risk.

high-performance LEDs due to high photoluminescence (PL) quantum efficiency, narrow emission linewidth (i.e., high color purity), and low density of sub-gap electronic trap states. [6][7][8][9] Significant breakthroughs have been achieved in perovskite LEDs (PeLEDs) in the past 5 years, with the external quantum efficiency (EQE) boosted from 0.76% in 2014 to over 21% recently, [1,10,11] comparable to the stateof-the-art performance of organic LEDs (OLEDs). [12] Nevertheless, despite rapid development of electroluminescence (EL) efficiency, the commercialization of PeLEDs is still challenging due to the poor device stability, [13] which mainly stems from degradation of perovskite materials upon air exposure or electrical bias. As demonstrated in perovskite-based photovoltaic (PV) devices, migration of mobile ions under electrical bias stress causes destruction of the perovskite lattices and infiltration of mobile ions into adjacent layers. [14,15] In PeLEDs, a higher electricfield is present and may aggravate the ion migration issue. In particular, in contrast to the thick perovskite absorber layer in PV devices, the perovskite light-emitting layer in PeLEDs is much thinner (typically a few tens of nanometers) as required for spatial confinement of charge carriers and efficient radiative recombination. [1] Therefore, mobile ions in the thin perovskite layer would be The poor stability of perovskite light-emitting diodes (PeLEDs) is a key bottleneck that hinders commercialization of this technology. Here, the degradation process of formamidinium lead iodide (FAPbI 3 )-based PeLEDs is carefully investigated and the device stability is improved through binary-alkalication incorporation. Using time-of-flight secondary-ion mass spectrometry, it is found that the degradation of FAPbI 3 -based PeLEDs during operation is directly associated with ion migration, and incorporation of binary alkali cations, i.e., Cs+ and Rb + , in FAPbI 3 can suppress ion migration and significantly enhance the lifetime of PeLEDs. Combining experimental and theoretical approaches, it is further revealed that Cs + and Rb + ions stabilize the perovskite films by locating at different lattice positions, with Cs + ions present relatively uniformly throughout the bulk perovskite, while Rb + ions are found preferentially on the surface and grain boundaries. Further chemical bonding analysis shows that both Cs + and Rb + ions raise the net atomic charge of the surrounding I anions, leading to stronger Coulomb interactions between the cations and the inorganic framework. As a result, the Cs + -Rb + -incorporated PeLEDs exhibit an external quantum efficiency of 15.84%, the highest among alkali cation-incorporated FAPbI 3 devices. More importantly, the PeLEDs show significantly enhanced operation stability, achieving a half-lifetime over 3600 min.In recent years, solution-processed metal halide perovskites have attracted tremendous interests in the scientific community including the field of light-emitting diodes (LEDs). [1][2][3][4][5] Besides low fab...